Educators seek to develop students' mathematical knowledge retention to increase student efficacy in follow-on classwork, improvement of test scores, attainment of standards, and preparation for careers. Interactive visuals, feedback during problem solving, and incorporation of higher-order thinking skills are known to increase retention, but a comparison of online and face-to-face learning regarding knowledge retention has not been fully explored. The current study tested 38 Caucasian eighth grade students for knowledge retention on ten mathematical topics they had learned in sixth grade during either online or faceto-face conditions. After two years, students were given the same posttest as in 6th grade over the 10 units of which five had been learned online and five face-to-face. Scores for long-term gain scores showed no significant differences between online or face-to-face learning conditions. A TOST calculation was used to show equivalence of middle school student long-term learning across online and face-to-face conditions in mathematics in this study within the limits of the test. The interactive nature of each condition contributed to strong mathematical understanding, which led to the retention being equivalent for both conditions.